This invention relates to electromagnets for a high power attenuator using a programmable microwave circulator. and more particularly to a core design for the electromagnets used in phase shifters having ferrite slabs in waveguides.
Phase shifters and other microwave devices having ferrite slabs in a waveguide, with biasing or control magnets are well known. For example, U.S. Pat. No. 3,101,458 to Chandler et al to discloses ferrite elements mounted on opposing walls of the waveguide. U.S. Pat. No. 3,401,361 to Schloemann discloses a reciprocal phase shifter having discrete ferrite bodies providing a symmetrical distribution of magnetization states about the center plane of a waveguide transmission structure. Also of general interest are U.S. Pat. Nos. 3,761,845 to Ajoika et al and 3,594,812 to Buck which disclose ferrite phase shifters.
The advantages of electronic programmable high power microwave differential phase shift circulators are many. Such control permits rapid high-power switching, power splitting, or continuously or stepped variable attenuation with minimal phase modulation. The disadvantage of most electromagnetic circulators is that they weigh much more than a comparable permanent magnet type for the same power rating. The weight of programmable circulators restricts their use in aerospace and spacecraft applications where weight is an important consideration.
In some advanced high-power transmitter applications, it is necessary to control output peak power as a function of a particular system parameter. As a result of the unavailability of low loss, high power, microwave analog attenuators with low phase distortion, it has been proposed to design an attenuator with the amplitude control function in the low level portion of the transmitter amplifier chain. While the ability to control output power at low levels would at first appear to be an advantage, this approach imposes severe constraints on the properties and tolerances of subsequent RF devices in the transmitter chain, resulting in a negative impact on the yield of expensive components. The availability of a high peak and average power attenuator with low loss, low phase distortion, and fast switching would allow all the elements of the transmitter chain to operate close to their optimum efficiency and maximum stabitlity points.